For the past four years, Google has been working on self-driving cars with a mechanism to return control of the steering wheel to the driver in case of emergency. But Google's brightest minds now say they can't make that handoff work anytime soon.

Their answer? Take the driver completely out of the driving.

The company has begun building a fleet of 100 experimental electric-powered vehicles that will dispense with all the standard controls found in modern automobiles. The two-seat vehicle looks a bit like the ultracompact Fiat 500 or the Mercedes-Benz Smart car if you take out the steering wheel, gas pedal, brake and gear shift. The only things the driver controls is a red "e-stop" button for panic stops and a separate start button.

The car would be summoned with a smartphone application. It would pick up a passenger and automatically drive to a destination selected on a smartphone app without any human intervention.

Google won't say if it intends to get into the car manufacturing business or simply supply technology to carmakers, but it says there are plenty of possibilities if it can persuade regulators to allow cars with no drivers. One potential use: driverless taxi cabs.

In an interview at Google's headquarters here, Sergey Brin, a Google co-founder who is actively involved in the research program, said the company decided to change the car project more than a year ago after an experiment in which Google employees used autonomous vehicles for their normal commutes to work.

There were no crashes. But Google engineers realized that asking a human passenger - who could be reading or daydreaming or even sleeping - to take over in an emergency won't work.

The new Google strategy for autonomous cars is a break from many competing vehicle projects. Mercedes, BMW and Volvo have introduced cars that have the ability to travel without driver intervention in limited circumstances - though none completely eliminate the driver.

That feature, which is generally known as Traffic Jam Assist, allows the car to steer and follow another vehicle in stop-and-go highway driving at low speeds. In the Mercedes version, the system disengages itself if the driver takes his hands off the steering wheel for more than 10 seconds.

Volvo said that by 2017 it planned to have the cars in the hands of ordinary consumers for testing in the streets of Gothenburg, Sweden.

This image provided by Google shows a very early version of Google's prototype self-driving car. The two-seater won't be sold publicly, but Google on Tuesday said it hopes by this time next year, 100 prototypes will be on public roads. AP Photo/Google